The correct answer is B, presidential primaries. Let's think about why is that: what is the difference between B and the other options?
When we are talking about congressional legislative actions, public policy debates, and Supreme Court rulings, we can hardly have a real conversation with only two possible answers. Public debate is necessarily complex and multilayered; and the main goal isn't one thing or another to win, most of the times, but to achieve the best possible result.
So the press takes advantage of presidential primaries, when besides public debate also individual figures are central and covers it like a horse race. Coverage then gets less political, since it doesn't have much space for healthy and serious debates, and becomes only about the disputing figures.